Regulators are the low slot shield item.

I don't really see how adding another module would add much more than SP sink

A complex PG mod adds 11% PG at the very minimum to any suit as it it (flat increase of 11 on max skilled Logistics w/ 102 total).
As for the rest, well, the regulators are presumably intended to add a useful amount of EHP over time to a shield tank; balancing those better would go miles, I think.

Split Infantry power mods into 2 types.

Reactor control units (high direct % increase of PG [10 to 15%])
Power diagnostic systems. (small direct % PG increase [3 to 5%], small % shield HP buff [3 to 5%], small % shield recharge rate [5 to 8%] )

I'm not going to get into any numbers about balance, but making a lowslot shield module would make shield.

Power diagnostic system modules for vehicles were awesome, they helped out shield tanks by letting the fit their shields and gave a little boost to shield HP. To those saying this conflicts with regulators, they don't since regulators only make shield recharge delays and not shield HP or recharge rates better.

We really need low slot modules that are useful for shield tankers that don't necessarily encourage hybrid tanking.

You have defended the status quo with a tautology. "Regulators are the lowslot shield item, therefore don't change lowslot shields"

My argument is that since PG has been a limiting factor in shield effectiveness and increasing PG efficiency for shields would only increase the likelihood that players hybrid tank, then making some kind of small shield buff that neutralizes this would probably be effective.

...currently working out some reasonable ways to represent the trade off here, but, there should be a threshold where lowslot investments in this kind of shield upgrade on a shield suit, would provide a better eHP buffer and/or eHP over time than just a switch to armor for hybrid tanking.

I'm going to do some study once the new shield modules come out.